python 详解类class的通过__slots__限制类实例对象的属性（七）

当我们通过一个类创建了实例之后，仍然可以给实例添加属性，但是这些属性只属于这个实例。有些时候，我们可以需要限制类实例对象的属性，这时就要用到类中的_ _slots _ _ 属性了。_ _ slots_ _属性对于一个tuple，只有这个tuple中出现的属性可以被类实例使用。

class person(object):
    __slots__ = ("name", "age","weight")
    def __init__(self, name, age, weight):
        self.name = name
        self.age = age
        self.weight = weight
Bruce = person("Bruce", 25,60)        
print("%s is %d years old and he weights %s" %(Bruce.name, Bruce.age,Bruce.weight))
Bruce.tall = 180

Bruce is 25 years old and he weights 60

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
 in ()
      7 Bruce = person("Bruce", 25,60)
      8 print("%s is %d years old and he weights %s" %(Bruce.name, Bruce.age,Bruce.weight))
----> 9 Bruce.tall = 180

AttributeError: 'person' object has no attribute 'tall'

person类实例化后，Bruce不能添加新的属性，_ _ slots_ _属性对于一个tuple属性赋值，只有这个tuple中出现的属性可以被类实例使用

• 使用_ _  slots _ _ 要注意， _ _ slots_ _定义的属性仅对当前类的实例起作用，对继承的子类实例是不起作用的,不会限制继承的子类实例化再添加新的属性

class human(object):
    __slots__ = ("name", "age","weight")
class person(human):
    #__slots__ = ("name", "age","weight")
    def __init__(self, name, age, weight):
        self.name = name
        self.age = age
        self.weight = weight
Bruce = person("Bruce", 25,60)        
print("%s is %d years old and he weights %s" %(Bruce.name, Bruce.age,Bruce.weight))
Bruce.tall = 180

Bruce is 25 years old and he weights 60

• 如果子类本身也有_ _ slots_ _ 属性，子类的属性就是自身的 _ _ slots _ _ 加上父类的_ _ slots_ _

class human(object):
    __slots__ = ("tall")
class person(human):
    __slots__ = ("name", "age","weight")
    def __init__(self, name, age, weight):
        self.name = name
        self.age = age
        self.weight = weight
Bruce = person("Bruce", 25,60)        
print("%s is %d years old and he weights %s" %(Bruce.name, Bruce.age,Bruce.weight))
Bruce.tall = 180
print("%s is %d years old and he weights %s and he\'s tall is %s" %(Bruce.name, Bruce.age,Bruce.weight,Bruce.tall))
Bruce.appearance = 'handsome'

Bruce is 25 years old and he weights 60
Bruce is 25 years old and he weights 60 and he's tall is 180

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
 in ()
     12 Bruce.tall = 180
     13 print("%s is %d years old and he weights %s and he\'s tall is %s" %(Bruce.name, Bruce.age,Bruce.weight,Bruce.tall))
---> 14 Bruce.appearance = 'o,no'

AttributeError: 'person' object has no attribute 'appearance'

父类 和 子类 限制的 元组里面的变量属性都是可以生成调用 的。appearance 既不在父类也不再继承的子类 的元组列表里， 不能生成